The base, the back, the front of the lens against the filter ring, the side of the camera?
I'm talking of a permanent mounting, like the one on my Linhof STIV where it's built into the body. There just isn't room on a 35. I never use the level though, I prefer to use the gridlines I put on the GG. I do use the two tubular bubble levels built into the tripod head to set the tripod up level.